Addition of Polish translation for Digital

[Kshyhoo67]

Hi Helmut,

I have prepared a Polish translation for the "Digital" simulator. I would like to contribute these strings to the project to make it more accessible for Polish-speaking users.

I have followed the existing naming conventions and kept the original quotation marks and formatting as required.

Below are the translated strings (or I can create a Pull Request if you prefer):

lang_pl.xml

Thank you for creating such an amazing tool!

Best regards, Kshyhoo

[activityworkshop]

I'm also not sure how to create a Pull Request given the number of active forks right now.
So here's my attempt at cleaning up the German and English texts, maybe someone can incorporate them.

lang_de.xml
lang_en.xml